Various types of slitter rewinder machine are in use, each having advantages and disadvantages and each being suited to and manufactured for particular applications. These types of machine can be categorised according to their rewinding geometry, including centre wind, centre wind with contact lay-on, surface wind, centre surface wind and constant-gap winding. These geometries are illustrated respectively in FIGS. 1 to 5, showing the rewind reel 2, web 4 and contact roller 6 (if present).
Centre winding (FIG. 1) is the simplest geometry, the reel itself being driven and the web being drawn tangentially onto the reel. A machine using this arrangement is simple to operate and unload and can run at high speed. However, there is a tendency for air to be trapped beneath the web as it is drawn onto the reel. This reduces the precision of winding and renders this technique unsuitable for certain web materials and web widths.
Centre winding with contact lay-on (FIG. 2) reduces the entrapment of air, the air being excluded by the pressure between the lay-on roller and the reeled web. This arrangement improves accuracy but still can not be used with certain web materials, such as fragile or elastic materials.
These centre wind geometries are typically used in duplex centre winding machines, in which reels may be wound on either of two laterally-spaced parallel shafts. This enables a wider web (carried on a third parallel shaft) to be slit into a plurality of narrower webs, adjacent narrower webs being rewound onto alternate rewind shafts of the duplex centre winder.
In a surface winder (FIG. 3) a lay-on, or contact, roller is used but the lay-on roller is driven and the rewind reel is not. The pressure of the lay-on roller on the surface of the rewind reel is sufficient to drive the rewind reel. This system has the advantage that the web can be wound onto the rewind reel under very low tension. This is suitable for fragile or elastic web materials.
Centre surface winding (FIG. 4) entails the use of a lay-on roller but both the lay-on roller and the rewind reel are driven. This allows optimum control of the web tension on the rewind reel but increases the complexity and cost of the machine compared with a simple centre wind system. In particular, reel loading and unloading is more complicated and so reel change over times are disadvantageously long.
In constant gap winding (FIG. 5), an idle roller is used for guiding the web onto the rewind reel during centre winding. The idle roller does not contact the rewind reel but is moved away from the rewinder reel shaft during winding so as to keep constant the distance travelled by the web between the idle roller and the rewind reel.
The performance of these conventional rewind machines is becoming more of a problem as environmental pressures require reduced waste and reduced quantity of packaging materials (for which web materials are commonly used), which leads to the development of web materials having higher barrier properties, thinner films and papers, and environmentally friendly inks. Such materials become more difficult to handle and therefore expose the limitations of conventional rewinding machines.